The present invention relates to a PCM signal recording technique, and more particularly to a method and apparatus for recording PCM audio signals on a VTR recording medium, such as a magnetic tape, in a plurality of different transmission rates.
In the 8-mm VTR, widely used is an apparatus which quantizes an audio signal in 10-bit units, compresses this 10-bit signal to an 8-bit PCM signal, and records the 8-bit PCM signal.
A conventional 8-mm VTR apparatus, such as described in JP-A-64-86304, provides an index area between a postamble area and a video-PCM guard (V-P guard) band area, and records therein index codes, called video subcodes, including a search signal used for reproducing a video signal, a recording date, an absolute position, a program number and so on, so as to permit a starting position detection for a search replay.
On the other hand, as a PCM audio signal, a PCM signal quantized in 16-bit units is compressed, depending on the kind of a magnetic tape, to reduce the data amount, and is recorded on the magnetic tape by changing the transmission rate, as described in U.S. Pat. No. 4,961,204 issued to Tanaka et al and JP-A-1-276471. The 8-mm VTR thus handles PCM signals at three different transmission rates.
The above-mentioned conventional apparatus for recording a 10-bit quantized PCM signal records index codes at the same transmission rate as that of a 10-bit quantized PCM signal, and does not consider compatibility with an apparatus for recording PCM signals in a plurality of transmission rates, so that the index codes cannot be added to a 16-bit quantized PCM signal having a different transmission rate from that of the 10-bit quantized PCM signal.